1. Field of the Invention
The present invention relates to a process to reduce emissions discharge from a natural gas processing dehydration system. In particular, the invention relates to a self-contained natural gas processing system which eliminates discharge of gaseous hydrocarbons to the environment.
2. Prior Art
Natural gas processing systems are used to treat and purify raw natural gas that is obtained from subterranean locations and delivered to the surface. The treated natural gas is used in a wide variety of fuel applications.
The natural gas delivered to the surface contains primarily methane but also includes aromatic and other gaseous hydrocarbons including ethane, propane; butane, and pentanes, as well as carbon dioxide, hydrogen sulfide, mercaptans, nitrogen, water, water vapor, and liquid hydrocarbons, such as crude oil.
It is common practice and is necessary to process or condition the natural gas in the field near the wellhead in order to remove some of these materials before transporting the natural gas. Removal of water and water vapors is necessary to prevent clogging of pipelines with liquid water and liquid hydrocarbons which may separate, to prevent formation of methane hydrates, and to prevent corrosion of tanks, pipelines and other metal equipment.
In a typical natural gas processing dehydration configuration, a separator is used to separate the natural gas from the water and water vapor. A liquid desiccant absorbs the water, moisture and absorbable hydrocarbons in the separator and then the natural gas is removed and transported for use. Examples of liquid desiccant include diethylene glycol and triethylene glycol. The moisture rich desiccant is then processed through a dehydrator to remove the water moisture and absorbed hydrocarbons so that the desiccant may be recycled. In the past, gaseous emissions were released to the atmosphere and liquid emissions containing hydrocarbons were dispersed off. Increasingly, it is unacceptable to release hydrocarbons into the environment.
There have been a number of previous proposals to reduce polluting emissions from natural gas processing systems. Hill et al. (U.S. Pat. No. 5,665,144) proposes reclaiming uncondensed hydrocarbons normally exhausted to the atmosphere. Water and hydrocarbon liquid, however, are simply sent to a storage container which remains and requires disposal.
Choi (U.S. Pat. No. 5,163,981) proposes controlling discharge of pollutants from natural gas dehydrators, however, water and entrained hydrocarbon gas is simply separated out by the system and requires proper disposal.
Accordingly, the present invention provides a novel system and process in order to reduce emissions from a natural gas processing system.
The present invention also provides a self-contained natural gas processing system that will dispose of any liquid hydrocarbons and hydrocarbon gas generated during the processing.
The present invention also provides a natural gas processing system wherein separated water and hydrocarbon gas is used in the reboiler to control the temperature in the reboiler.